1. Field of Invention
The invention is concerned with removing adhering substances from articles which have undergone a chemical or electrochemical treatment, for example (but not exclusively) in galvanizing baths.
More particularly, the invention is concerned with a novel method of effecting such removal, an apparatus for carrying out the method, and an arrangement for the chemical or electrochemical treatment of articles which utilizes the apparatus.
2. The Prior Art
There are many chemical or electrochemical surface treatments, following which the treated articles must be freed of a substance adhering to them from the treatment, e.g., a bath residue. An important treatment of this type is the galvanizing treatment. For purposes of explanation the invention will hereafter be described with reference thereto, although it should be understood that it is not so limited.
During galvanization an article must be dipped into a series of galvanizing baths, each containing a substance for the active surface treatment of the article. It is almost always necessary to thoroughly remove from the article the adhering residue of the preceding bath before the article can be immersed in the subsequent bath. This rinsing of the articles between the successive galvanic treating stages is an important factor, both with respect to the quality of the finished product (improperly rinsed articles are not properly treated in subsequent stages) and to overall cost (this factor will be explained subsequently).
The rinsing agent thus employed is usually water. Such water may be drawn from a municipal water supply or it may be water that is recirculated in a closed system and processed in an ion-exchange installation.
Water received from the unicipal supply must be purchased by the user. Since this involves considerations of expense, it is desired to use as little such water as possible, a requirement which is in contradiction to the conventional wisdom that the more water is used, the better will be the rinsing effect. Also, once the water has been used for rinsing it is enriched with the rinsed-off residue which is often of a poisonous character. Before such water can be discharged into a muncipal sewage system it must be neutralized or the poisonous substances must be removed. This, also, causes expenses which are added to those of purchasing the water in the first place; evidently, the more water is used for rinsing, the higher will be the overall costs.
If the rinsing water is recirculated in a closed system and processed in an ion-exchange installation, none or very little of the rinsing water will be lost. It is therefore possible to use as much rinsing water as desired. However, ion-exchange installations represent a very expensive investment and must be the larger, the more water is to be processed and also in dependence upon the types of concentrations of residual substances with which the water becomes enriched during rinsing of the articles.
As a general rule, the decision to use municipal water or to purchase a closed-circuit ion-exchange installation will be a question of economics. If it is possible to effect the necessary rinsing with only small quantities of water, then it is usually less expensive to purchase municipal water and to detoxify it before discharge into the sewage system (or before using it to compensate for evaporation losses of the treating bath or baths).
The problem is how to keep the required water quantity small. It is known that this is possible only if the water is enriched with the rinsed-off contaminants to as high a degree as possible before it must be detoxified and discharged or re-used. Several proposals have, in fact, been made in the prior art to achieve this purpose.
For example, it has been proposed to dip the articles into a container filled with rinsing water. Practical experience has shown that the required rinsing effectiveness cannot be achieved with a single rinsing container following each container of treating bath. It is therefore customary practice to arrange subsequent to each treating bath several rinsing containers which are usually connected in cascade form and wherein the water travels about the article to be rinsed. Water travel is in counterflow to the movement of the article from one into the next container, so that the water becomes progressively enriched with the residual (treating) substance that is being flushed from the article. This is then usually followed by a final container in which the article is allowed to soak in still water for a time. The previous practice has been to use three such containers arranged consecutively; more recently up to eight containers have been used and this has resulted in a noticeable decrease of the water requirement (since the adhering bath residue is removed more efficiently and a higher concentration of it can be achieved in the rinsing water before the same must be discharged). However, such an installation represents a substantial investment, particularly because cascading of the water is not practicable when so many containers are involved, so that the water must be pumped through the container series (which adds to the cost because it requires pumps, conduits, valves and energy to operate the pumps). In addition, there are certain process conditions (e.g. when rinsing is carried out subsequent to nickel plating) which do not permit the relatively long dwell time of the articles in the container that results from the use of a large number of such containers through which the articles must travel seriatim.
Another proposal in the prior art involves spraying rinse water against the articles, so as to flush away the adhering bath residue. This method is not uniformly suited for all types of articles; however, flat objects such as e.g. circuit boards or conductor plates can be well cleaned this way. The spray method does result in reduced water use and has the additional advantage of offering rapid and intimate mixing of the sprayed-on water with the ahering bath residue (this being a necessary condition for rapid and effective flushing-off of the residue). In the dip method, by contrast, it is usually considered necessary to blow air into the rinse water in the containers, in order to agitate the water and in this way to aid the residue removal. However, despite its advantages the spray method is not widely used because the required installations are relatively expensive and require an often unacceptable capital investment.
In summary, therefore, it can be said that the state of the art is in need of further improvement.